The present invention relates generally to medical informatics, and more particularly to real-time acquisition, storage, and retrieval of digital images.
Development of real-time image analysis techniques has led to major advances in medical diagnostics. For some applications, static images are adequate; for example, an X-ray of a bone fracture. For other applications, however, streaming images provide more comprehensive information. Consider heart disorders, for example. For functional analysis, real-time dynamic X-ray angiography provides streaming images of the blood vessels while blood is flowing through them, as the heart is beating.
The output of many medical instruments, such as X-ray and Magnetic Resonance Imaging (MRI) diagnostic units, is a stream of digital image data from which dynamic images are created. Requirements for high spatial and temporal resolution produce large files which need to be processed in real time. Spatial resolution is a function of pixel density. Temporal resolution is a function of frames per second. As an example, a frame comprising 1024×1024 pixels with a pixel depth of 2 bytes requires approximately 2 Mbytes. At a frame rate of 30 frames/second, the data rate is approximately 63 Mbyte/second. A video record requires approximately 3.8 Gbyte for a 1-minute record. Herein, the term “frame” refers to a set of pixels of a defined matrix size.
Many equipment providers have proprietary systems for processing streaming digital image data into streaming images. To provide compatibility among different equipment providers, however, the Digital Imaging and Communications in Medicine (DICOM) standards have evolved. A DICOM standard specifies the format for encoding pixel data. Conformance to DICOM standards is a major goal of manufacturers of medical digital imaging equipment. Another goal of equipment manufacturers is to reduce costs by using common platforms, such as workstations running on a Windows operating system (OS), instead of custom hardware and software.
As discussed above, acquisition and storage of streaming digital image data entails large amounts of data being stored to persistent storage media, such as a hard drive, in real time. Full-rate playback of streaming images from digital image data stored on persistent media also requires high data transfer rates. Standard processing of input/output (I/O) by a native OS is too slow and may result in data being lost during acquisition and storage. One option is to bypass an OS altogether and map the digital image data directly onto hard disks using a proprietary file system that increases the transfer rate of the disk drive. The format of these files, however, do not conform to DICOM standards. What is needed is an image file system for acquisition and storage of real-time streaming digital image data on persistent storage media, and for full-rate playback of images stored on persistent storage media. An image file system which saves files in a format conforming to DICOM standards is desirable.